Current studies are focussed on the interfacial behavior of cell-membrane fatty acid spin-label and fluorescent probes. These studies are being carried out using monomolecular films at the air-water interface as well as liposomes as model membrane systems. The nitroxide fatty acids were found to affect their host lipid in a manner dependent on the host lipid polar group. While all the probes fluidized a fatty acid host lipid, this was complicated by an oxazolidine-choline specific interactions when lecithin was used as a host. The anthroyl fluorescent probes similarly fluidize or perturb a lecithin host lipid with decreasing effect as the anthroyl group is moved from the carboxyl to the methyl group for both monolayers and bilayers. Other work involves the miscibility and fluidity of mixed films and the condensing effect of dimethyl sulphoxide on phospholipids.